In recent years, many plated products comprise a molded plastic substrate which is first electrolessly plated and then electrolytically plated.
In conventional electroless plating processes, the plating substrate is first etched with a strong oxidizing acid or base. The etched substrate is then immersed in a solution containing a noble metal catalyst, e.g., a tin-palladium catalyst. If required, the substrate is then immersed in an activator solution, e.g., exposing the palladium of the tin-palladium catalyst. Finally, the activated substrate is immersed in an autocatalytic electroless plating solution where an initial coating of a conductive metal, such as copper or nickel, is established on the substrate by chemical deposition.
In a conventional electrolytic plating process, the electrolessly plated plastic substrate is first immersed in cleaning solutions and then activated by immersion in a dilute acid solution, e.g., a dilute sulfuric acid solution. It is then immersed in one or more electroplating baths wherein metal is deposited on the surface of the substrate electrolytically. In many applications, for example, layers of copper, nickel, and chromium are plated onto the substrate.
Conventional plating racks used in electroless and electrolytic plating processes comprise a metal framework having metal contacts for holding the plastic substrates on the rack. With electrolytic plating racks, the contacts also provide means for electrical communication between the racks and the plastic substrates. The plastic substrates are manually mounted on the contacts which hold the substrates firmly so that they do not fall off the racks in agitated plating solutions and, in the case of electrolytic plating racks, to provide uninterrupted electrical contact with the substrates.
The contacts are typically in the form of metal wire, rods, strips, and the like. Two or more contacts are usually used in a manner which applies pressure, generally in the form of a spring force or a gripping force, at two or more contact points on the substrate. These contact points are generally at locations on the substrate which are not seen when the substrate is assembled as a final product.
The number of substrates held by an electroless or electrolytic plating rack depends on the size of the rack, which is in turn usually dependent on the size of the plating tanks, and on the size of the substrates. It is not uncommon for an electroless or electrolytic plating rack to hold 25 or even 100 or more substrates. Since each substrate typically requires at least two rack contacts, it is apparent that such racks require a great deal of material and time to construct and are accordingly very expensive to build. Moreover, many substrates are difficult to hold and require complicated contact design. This further increases the expense of constructing the racks.
For very small substrates or for substrates which, because of their design, cannot be held directly by the rack contacts, the plating racks are designed so that the contacts grip or otherwise hold a runner or portion of a runner which is not removed from the substrate after it is molded. Here again, however, the rack must comprise separate contacts for each such runner. Such racks are expensive and time consuming to construct for the reasons mentioned above.
Not only are conventional plating racks expensive to build, their utility is restricted to the particular substrate or substrates for which it is designed. Once the production of that particular substrate is over, the use of that plating rack ceases and it must be discarded or rebuilt to hold a different substrate.